This invention relates generally to a system for producing and utilizing a stream of reactive gas species and, more particularly, to a plasma-assisted deposition system.
In many circumstances it is desirable to enhance the composition and quality of deposited semiconductor films. Plasmas or glow discharges have been used in conjunction with the deposition of semiconductor films for these purposes. For example, deposition has been carried out in the presence of a glow discharge containing one or more elements of the deposited film. The discharge is generated within the deposition environment, constraining the pressure and temperature therein to levels which can support the glow. Two recent systems of this type are described in Habermeier, Thin Solid Films, 80 (1981) 157-160, and Avaritsiotis et al., Thin Solid Films, 77 (1981) 351-357. Although these publications are dated after the conception date of the present invention, and are therefore not prior art to it, the underlying concept of generating a plasma or glow discharge within a deposition environment is prior art. The Habermeier and Avaritsiotis, et al. articles describe this concept as it relates to the deposition of particular transparent conducting films.
Another application of plasma technology to a deposition process involves the use of a plasma torch to spray polycrystalline semiconductor films onto substrates, as disclosed in Janowiecki et al. U.S. Pat. No. 4,003,770. In the Janowiecki et al. disclosure, a plasma is generated in a pressurized stream of "plasma forming gas" to produce a downwardly directed plasma jet. A semiconductor material such as silicon is fed into the plasma stream in the form of granules and is carried thereby to a substrate for deposition. The granules are melted by the plasma torch and sprayed by the torch onto the substrate. Silicon carried by the plasma stream exists as a number of discrete masses of silicon, in either the solid or liquid phase, until formed into a continuous film on the substrate.
Plasmas have also been used for the purpose of etching semiconductor materials, as described in Horiike, et al., "Proceedings of the 7th Conference on Solid State Devices," Tokyo, 1975, Supplement to Japanese Journal of Applied Physics, Volume 15 (1976). Horiike, et al. uses a plasma created by an electrical discharge in a CF.sub.4 --O.sub.2 mixture to etch films of various solid state materials, working primarily with a plasma produced in a main etching chamber. However, an experimental apparatus is also described in which a plasma produced within a first chamber is passed to a separate chamber for etching. This is done to investigate the dependence of etch rate on gas pressure. The teachings of Horiike, et al., are specific to the purposes of etching.
Therefore, it is desirable to provide an effective and versatile system for enhancing the composition and quality of deposited semiconductor films.